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Analog IC Design First – A OPAMP Design
Example.
報告人：何建興
Date: 15th NOV, 2007
Agenda
1. What is Analog Signal?
 2. Elements Used in Electronic Products.
 3. Why OPAMP.
 4. How an OPAMP works.
 5. What is MOS? MOS Basic Characteristic.
 6. A Design Example.
 7. Is It the best design?
 8. Is Direct Shrink Possible?
 9. Q&A
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What is Analog Signal?
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Analog signals in Integrated Circuits can
be in the form of Voltage or Current (or
Power).
They are continuous signals, (amplitude
vs. time). Voice and Audio signals are
good examples of analog signals.
If a threshold was set, then an Analog
signal can be easily converted to Digital
signal.
Example: A D AD_DA
Elements used in Electronic products
Resistors, Capacitors, Inductors,
Transistors and Diodes are basic devices
(elements) in Integrated Circuit.
 Many basic building blocks (IP) can be
composed of these devices.
 Ex: 1. RAM’s basic devices – MOS(RAM
cell + logic circuit, sense Amp.) +
Capacitors.
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2. Logic circuit – CMOS. (PMOS +
NMOS)
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3. USB interface – MOS + Resistors.
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Elements used in Electronic products
(continued)
4. Recorder (ADC), Player (DAC) – MOS
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+ Resistors + Capacitors.
 5. Regulator – MOS + Resistors.
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6. ESD PAD – MOS + Diode + Resistors.
The IP (Intellectual Property ) listed
above are able to construct a MP3
player Chip.
 Example: 1 2 3 4
 Many Analog blocks need OPAMP.
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WHY OPAMP?
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1. OPAMP (Operational Amplifier) are one
of the most important building blocks in
Analog IC design. It can be used to do
addition, subtraction, multiplication,
logarithm, …operations.
Filters, Integrators, Oscillators
Regulators, … etc. all include OPAMP.
Symbol of OPAMP
Examples:
How An OPAMP Works?
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1. There are 5 nodes on an OPAMP, they
are Positive (V+) terminal, Negative (V-)
terminal, Output (Vo) terminal, Power
(VDD) and Ground (GND).
2. An ideal OPAMP characteristic:
(I) infinite input resistance.
(II) infinite open loop gain.
(III) v+ = v- when negative feedback
configuration.
How An OPAMP Works? (continued)
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3. An real CMOS OPAMP can have:
(I) Very large input resistance (Ri) >1M
ohm.  input current =0
(II). Large but not finite open loop gain
(A) > 1000 (60dB).
4. Examples:
5. Insight
What is MOS? MOS Basic Characteristic.
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MOS : Metal –Oxide-Semiconductor
Example
A Design Example.
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1. Specification:
given a voltage 1.25V, design a OPAMP to
achieve 2.5V output.
Precision +- 1mV, : means A0>1000.
settling time < 1us, means ft>1M.
2. Schematic:
Is It the best design?
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1. The MOS size (aspect ratio) which we just
designed is not the unique solution. We can
do it better.
Based on the design we just finished, we can
tune the MOS size to achieve: (i) smaller area
(ii) consume less current. Both goals are the
popular topic on SoC for the Cost issue.
They are many methods to optimize this
design, only if they are immune to process
variations.
Is Direct Shrink Possible?
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